Conventionally, a power distribution system for distributing an AC power and a DC power in a building such as a house, a store or an office building, is disclosed in, e.g., Patent Document 1. The power distribution system is a grid-connected system that includes a DC power generation equipment such as a solar photovoltaic power generation apparatus, as a private power station, installed in a building. The power distribution system converts a DC power outputted from the DC power generation equipment into an AC power, and performs a grid connection of the AC power converted from the DC power of the DC power generation equipment and a commercial power source (an AC power system) supplied from an electric power company.
Such a grid-connected system employs a configuration where a DC power generated by the DC power generation equipment is converted into an AC power by a power converter (a power conditioner) and is cooperated with the commercial power source serving as an AC power source. Further, the grid-connected system enables a surplus power to reversely flow into the commercial power source (so-called electric power selling) when a power supplied from the DC power generation equipment exceeds the power consumed by loads within a building.
Furthermore, as a power distribution system for supplying a DC power to a DC load device, there is proposed a power supply system in, e.g., Patent Document 2. In the power supply system, a DC power supply unit communicates with a terminal device of the DC load device and a power-feeding control unit compares power reception information notified by the terminal device with operational power information stored in an operation information memory, and controls an output voltage to supply the DC load device with a proper voltage and current.
In such power distribution system for distributing the DC power, multiple power sources including a DC power generation equipment such as a solar photovoltaic power generation apparatus or a fuel cell, a battery, a commercial power source and the like, may be used. Therefore, it is necessary to provide a power distribution system suitable to these multiple power sources. In this case, typically, an output converter such as a DC/DC converter or an AC/DC converter is provided for each of the power sources, and outputs a DC power with a specific voltage level.
As described above, if there are used multiple power sources, the output converter such as a DC/DC converter or an AC/DC converter is required in order to distribute a power from the power sources. Thus, it is necessary to simplify and make safe the management of the plurality of power sources, such as installation and maintenance. In particular, since a plurality of heat-generating output converters is provided on a distribution board, a problem of heat dissipation property arises in a DC distribution board, unlike an AC distribution board.
Recently, there are provided an AC input terminal from an AC power source, a DC input terminal from a DC power source such as solar cells, and a DC output terminal connected to DC device all together in the distribution board. An erroneous connection between the terminals may lead to damage of devices and a serious accident, and cause danger.
Furthermore, a power distribution system disclosed in Patent Document 3 adopts a configuration for controlling the output of a secondary battery or solar cells so that a power converter or AC/DC converter can be operated at maximum conversion efficiency. Besides, in the power distribution system of Patent Document 3, multiple AC/DC converters are used depending on an amount of a power supplied to a load.
In the power distribution system of Patent Document 3, however, if the amount of the power supplied to the load varies due to, e.g., an increase of a load or a replacement of a load, the existing power converter cannot supply enough power to the load. Further, in a power distribution system having a specification where a power conversion efficiency increases with an increase in the amount of the power supplied to a load, a power conversion efficiency may lower due to a significant change in the amount of the power supplied to the load.
Such problem can be solved by changing the specification of the power distribution system in accordance with the load. In this case, the entire power distribution system has to be replaced. As a result, the existing power distribution system needs to be discarded, thereby causing an increase in cost.